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We investigate the axisymmetric slow viscous liquid flow around a spherical bubble located on the axis of a long circular tube analytically based on the Stokes approximation. The bubble translates along the axis of the tube with a constant velocity within Hagen–Poiseuille flow flowing far from the bubble. The translating velocity of the bubble and mean velocity of the Hagen–Poiseuille flow are given arbitrarily. To analyze Stokes equation, we use the method of complex eigenfunction expansions and the method of least squared error. As results, the streamline patterns and the pressure contour lines in the flow field are drawn for some radii of the bubble. The drag exerted on the bubble and the pressure change induced by the bubble are determined according to the radius of the bubble. For a small bubble radius in the tube, we compared results with previous asymptotic results. The drift velocity of the bubble due to the Hagen–Poiseuille flow in the circular tube is calculated according to the bubble radius. We show that extra pressure drop due to the drift bubble in the Hagen–Poiseuille flow becomes positive or negative depending on the radius of the bubble. When the bubble moves along a circular tube in the absence of the Hagen–Poiseuille flow, a series of viscous toroidal eddies appears in the anterior and posterior directions of the bubble. Moreover, we discuss the pressure and normal stress distributions on the bubble surface, which depend on the radius of the bubble. [ABSTRACT FROM AUTHOR]

Taking into account new problems arising in the transportation of a steam-water heat carrier to support operation of geothermal power plants (GeoPP), a procedure is outlined for determining the void fraction considering the gravity component of the pressure drop in the hydraulic design calculations of steam-water piping. Unavailability of data on the void fraction under the conditions of geothermal heat carrier transportation is noted. The drift flux model determining the steam velocity averaged over the channel cross-section was used to solve the formulated problem for upward flows. The factors affecting the distribution parameter and the drift velocity are reviewed. It is noted that the drift velocity depends not only on the gravity force but also on the hydrodynamic effect, which can be taken into account using the advanced distribution parameter. A similar approach has been proposed for downward flows according to which the liquid phase velocity averaged over the channel cross-section is calculated using equivalents of the empirical coefficients determined from the condition of equality of the parameters calculated for the upward and downward flows as applicable to the horizontal flow. The empirical values included in the recommended calculation formulas have been established. The proposed recommendations have been used in developing a computer code for the hydraulic design of pipelines. In addition to the gravitational pressure drop, the code also calculates the pressure drop due to friction or local resistance using formulas, which offers good agreement with the experimental data. To verify the model used in the program for the calculation of the gravitational pressure drop, the predictions were compared with the experimental data of the pressure drop across the pipeline from the Geo-1 well to the Verkhne-Mutnovskaya GeoPP (Kamchatka), which is in operation and features the maximum height difference among all existing domestic pipelines carrying steam-water mixture. A good agreement was found between the predictions and the experimental data on pressure drops, which indirectly confirms the adequacy of the recommended procedure for determining the void fraction. [ABSTRACT FROM AUTHOR]

In this paper, we present a collection of results focussing on the transport properties of doped direct-gap inverted-band highly polar III-nitride semiconductors (GaN, AlN, InN) and GaAs in the transient and steady state, calculated by using nonlinear quantum kinetic theory based on a non-equilibrium statistical ensemble formalism (NESEF). In the present paper, these results are compared with calculations using Monte Carlo modelling simulations and experimental measurements. Both n-type and p-type materials, in the presence of intermediate to high electric fields, are considered for several temperatures and carrier concentrations. The agreement between the results obtained using nonlinear quantum kinetic theory, with those of Monte Carlo calculations and experimental data is remarkably good, thus satisfactorily validating the NESEF. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations (MCSs) of electron swarms in F2, Ar, and CF4 under ac (radio frequency) electric and dc magnetic fields ($\mathbf {E}(t)$ and $\mathbf {B}$ fields) crossed at a right angle are performed, and the periodic response of the electron drift velocity vector $\mathbf {W}(t)$ is depicted as an elliptic vector locus (EVL). The vector head of $\mathbf {W}(t)$ draws an ellipse synchronously to the alternation of the ac $\mathbf {E}(t)$ field. The tilt of the major axis of the EVL, which represents the Hall deflection, increases with $|\mathbf {B}|$ , and the ellipse drawn by $\mathbf {W}(t)$ takes its maximum around the $|\mathbf {B}|$ value resonant to the ac $\mathbf {E}(t)$ field. It is demonstrated that a theoretical approximation derived from a constant-collision-frequency (CCF) model predicts well the fundamental tendency of the $|\mathbf {B}|$ -dependent variation of the EVL of $\mathbf {W}(t)$ in the three real gases. The $\mathbf {W}(t)$ in F2 agrees well with the CCF model at low electric fields for its nature that the total collision frequency does not change significantly. On the other hand, those in Ar and CF4 deviate from the CCF model. This visual depiction using the EVL of $\mathbf {W}(t)$ is expected to be applicable to the estimation of the directional electron drift in inductively coupled magnetized plasmas and to the characterization of the $\mathbf {W}(t)$ response in real gases. [ABSTRACT FROM AUTHOR]

Monte Carlo algorithms are developed to simulate the electron transport in semiconductors. In particular, the drift velocity in GaN semiconductors is calculated, and a comparison with experimental measurements is discussed. Explicit expressions for the scattering probabilities and distributions of the scattering angle of electrons on polar optical and intervalley phonons, and acoustic deformation potential as well are given. A good agreement of the simulation results and the experimental measurements reveals that the M-L valley is located at 0.7 eV higher than the Γ-valley. This value agrees with other experimental studies, while it is lower compared to ab initio calculations. [ABSTRACT FROM AUTHOR]

Dynamic biological systems can be modelled to an equivalent modular structure using Boolean networks (BNs) due to their simple construction and relative ease of integration. The chemotaxis network of the bacterium Escherichia coli (E. coli) is one of the most investigated biological systems. In this study, the authors developed a multi‐bit Boolean approach to model the drifting behaviour of the E. coli chemotaxis system. Their approach, which is slightly different than the conventional BNs, is designed to provide finer resolution to mimic high‐level functional behaviour. Using this approach, they simulated the transient and steady‐state responses of the chemoreceptor sensory module. Furthermore, they estimated the drift velocity under conditions of the exponential nutrient gradient. Their predictions on chemotactic drifting are in good agreement with the experimental measurements under similar input conditions. Taken together, by simulating chemotactic drifting, they propose that multi‐bit Boolean methodology can be used for modelling complex biological networks. Application of the method towards designing bio‐inspired systems such as nano‐bots is discussed. [ABSTRACT FROM AUTHOR]

The innovative and highly effective Russian electrostatic precipitators of the ÉGAV type were created in order to solve problems associated with the reduction of ash emissions at coal power plants. The new electrostatic precipitators ensured an increase in precipitation effectiveness to 99.87% in the same overall housing sizes along with a reduction in emissions up to 16 times, with actual emissions ranging from 12.6 to 119 mg/m3 (under standard conditions). The technical solutions for intensifying electrostatic precipitation realised in ÉGAV precipitators increase particle drift velocity to the precipitating electrode by 65%. The application of the ÉGAV type electrostatic precipitators for removing high-resistivity ashes from flue gases led to the required reduction of emissions during the modernization of the acting electrostatic precipitators. The cost of reconstructing the gas-cleaning unit with the application of innovative electrostatic precipitators turned to be less than with the use of a combined electrostatic precipitator or a bag filter. The new electrical cleaning technology also formed a scientific basis for the innovative development of other promising gas-cleaning technologies. [ABSTRACT FROM AUTHOR]

The possibility of intensifying the processes in gas-dispersed systems with coagulated particles of different dimensions and the efficiency of air purification depend on the characteristics of the field created by electrodepositing plants. This work was carried out with a view of optimizing the parameters of electrodepositing systems to increase the rate of aerosol cloud deposition in an air medium. The theoretical and experimental studies are oriented to improving the methods of removing harmful aerosol formations in the air space by exposure to external electrostatic fields. This paper describes experimental investigation of coagulation and deposition of aerosol particles by inducing external fields in a closed volume with account for different technical parameters of devices for trapping different kinds of finely divided particles. To obtain the dispersed and concentration characteristics of aerosol, use is made of the method of searching for the solution in the form of a multiparameter function of the size distribution of particles realized as part of a laser measuring complex. [ABSTRACT FROM AUTHOR]

• The all-sky airglow imager and Digisonde data were used to investigate plasma bubbles. • Optical image processing was performed to obtain image products with high resolution. • Plasma bubbles appeared like long stripe and bifurcated vertically. • The distance between adjacent plasma bubbles was in the range of 100–400 km. • Plasma bubbles generally drifted eastward and the average drift velocity was 90 m/s. Ionospheric plasma bubbles and scintillation phenomena often occur at low latitudes in China. The all-sky airglow imager located at Fuke station in Hainan (19.5°N, 109.2°E) is part of the Meridian project in China. In this work, we used mainly the observation data obtained by the imager and a digisonde to study plasma bubbles. Optical image processing—including image enhancement, azimuth correction and image projection—was performed on the original airglow observation images, and clear high-resolution images of the bubbles were obtained. Based on these, the morphological features, spatial and temporal variations, spatial scale, drift velocity of the plasma bubbles in the F region of the ionosphere were investigated and analyzed. The plasma bubbles appeared as long, dark stripes on the bright airglow emission background. Their large-scale structures often bifurcated vertically, and were usually tilted westward with north-south extension along the magnetic field lines. The east-west scale of the plasma bubbles was usually greater than 200 km and these increased gradually with time. Moreover, the distance between the adjacent plasma bubbles also increased over time, and was in the 100–400 km range. Plasma bubbles generally drifted eastward with an average drift velocity of approximately 90 m/s. The occurrence and duration of the plasma bubbles were compared with digisonde observations, and it was shown that plasma bubbles lasted for nearly four hours. Additionally, the main characteristics of the plasma bubbles were obtained using both optical and radio observations and the study of which can be beneficial for monitoring and predicting ionospheric scintillations. [ABSTRACT FROM AUTHOR]

Due to the linear correlation between the subgrid drift velocity and the filtered drag force, modeling the drift velocity would be an alternative way to obtain the filtered drag force for coarse-grid simulations. This work aims to improve the predictability of models for the drift velocity using a new effective marker, the filtered gas pressure gradient, which is identified by momentum balance analysis. New models are constructed based on conditional averaging of the results obtained from fine-grid two-fluid model simulations of three-dimensional unbounded fluidized systems. A priori assessment is presented with the comparison between the proposed models and the best available Smagorinsky-type model with dynamic adjustment technique proposed in the literature. Results show that the proposed models give satisfactory performance. More important, the proposed models are demonstrated to have a better adaptability for cases under various physical conditions than the Smagorinsky-type model. [ABSTRACT FROM AUTHOR]

The high-field carrier transport properties of 4H-SiC including the impact ionization coefficients are theoretically analyzed based on a full-band Monte Carlo simulation. The simulation reasonably reproduces the behaviors of the impact ionization coefficients experimentally reported, such as temperature dependence, anisotropy, and the difference between electrons and holes. The mechanisms behind these behaviors are then discussed based on the band structure of 4H-SiC. [ABSTRACT FROM AUTHOR]

In this paper, some aspects of the determination of the concentration profile during diffusion in NiAl–Ti and CMSX4 systems are shown by means of numerical simulations. The results are compared with experiments. The bivelocity method is used to show the evolution of the three-component multiphase system. The simulations present that the local entropy production allows for determination of the profiles in complicated systems.

Thermohydraulic behavior in spent fuel pool is quite important in evaluating safety of a nuclear reactor under accidental conditions. Particularly, accurate prediction of void fraction in spent fuel pool is indispensable for evaluating cooling characteristics of spent fuel. In view of these, experimental and analytical studies were carried out for void fraction in spent fuel pool. The experiment was performed to measure the heat-up and void fraction transient during the postulated SFP accident. In this experiment, a simulated 7x7 BWR rod bundle that consists of 49 heater rods, 7 spacer grids and upper tie-plate was used. The measured data was compared with the some driftflux correlations under the low pressure and the low flow rate condition related to SFP accident. [ABSTRACT FROM AUTHOR]

Graphene nanoscroll introduced recently is another form of a graphene-based two-dimensional material, which is especially attractive in nanoelectronic applications. As carriers can travel ballistically or semi-ballistically, they can reach high-speed and energy if the channel length is enough. Therefore, they can collide and result in an excessive current called ionisation current. As a result, it is important to study this mechanism carefully. In this paper, we propose an analytical approach to calculate an ionisation coefficient. [ABSTRACT FROM AUTHOR]

The effect of high voltage electrostatic voltage on dust removal efficiency is studied. The dust removal efficiency of ESP can reach more than 90%, no matter the spacing of plates or the voltage between plates is changed. The maximum trapping efficiency is 99.66% when the maximum plate spacing and voltage are 32 kV. The volt-ampere characteristic curves of ESP under no-load and load are basically the same. Current increases sharply at about 9 kV, and flashover occurs at about 20 kV with the rapid increase of current. [ABSTRACT FROM AUTHOR]

This paper presents a computational comparison of the penetration capability of two shaped charges—with conical and hemispherical (degressive thickness) liners. It is shown that close values of the penetration capability of the charges are provided only in the ideal case of strictly axisymmetric motion of shaped-charge jets. [ABSTRACT FROM AUTHOR]

We investigate the axisymmetric slow viscous flow around a sphere located on the axis of a long circular cylinder analytically based on the Stokes approximation. The sphere translates along the centerline of the cylinder with a constant velocity within Hagen–Poiseuille flow flowing far from the sphere. The translating velocity of the sphere and mean velocity of the Hagen–Poiseuille flow are arbitrary constant. To analyze Stokes equation, we use the method of complex eigenfunction expansions and the method of least squared error. As results, the streamline patterns and the pressure contour lines in the flow field are drawn for some radii of the sphere. The drag exerted on the sphere and the pressure change by the sphere are determined as the radius of the sphere. For a small sphere radius and for a sphere fitted closely in the cylinder, we compared results with previous asymptotic results and lubrication theory results, respectively. The velocity of the drifting sphere by the Hagen–Poiseuille flow in the circular cylinder is determined as the sphere radius. The pressure change induced by the drifting sphere in the Hagen–Poiseuille flow is also obtained. When the sphere translates along the plugged circular cylinder, a series of viscous toroidal eddies appears each side of the cylinder expectably. Moreover, we discussed the pressure and shear stress on the sphere surface and showed some critical range of these stresses. [ABSTRACT FROM AUTHOR]

We consider the problem of a hopping ball excited by a travelling harmonic wave on an elastic surface. The ball, considered as a particle, is assumed to interact with the surface through inelastic collisions. The surface motion due to the wave induces a horizontal drift in the ball. The problem is treated analytically under certain approximations. The phase space of the hopping motion is captured by constructing a phasevelocity return map. The fixed points of the return map and its compositions represent periodic hopping solutions. The linear stability of the obtained periodic solution is studied in detail. The minimum frequency for the onset of periodic hops, and the subsequent loss of stability at the bifurcation frequency, have been determined analytically. Interestingly, for small values of wave amplitude, the analytical solutions reveal striking similarities with the results of the classical bouncing ball problem. [ABSTRACT FROM AUTHOR]

A theoretical study, by using Nonequilibrium Statistical Ensemble Formalism (NESEF), on the nonlinear transport of electrons in the transient and steady state of n-doped 4H-SiC under the influence of high electric fields is presented. The electron drift velocity and the nonequilibrium temperature are obtained, and their dependence on the electric field applied in the orientation parallel or perpendicular to the c-axis is derived and analyzed. [ABSTRACT FROM AUTHOR]

The processes of charge transfer in semiconductors are considered. A model is constructed based on the quantum kinetic equations for the distribution functions of conduction electrons and holes of the valence band in the phase space of coordinates and quasi-momenta. Scattering of charge carriers is modeled by the statistical particle method. The basic processes of electron scattering by lattice defects are considered. The calculations of the electron drift velocity in pure and doped silicon are presented. [ABSTRACT FROM AUTHOR]

Abstract Filtered two-fluid model (fTFM) for gas-particle flows require closures for the sub-filter scale corrections to interphase drag force and stresses, the former being more significant. In this study, we have formulated a neural-network-based model to predict the sub-grid drift velocity, which is then used to estimate the drag correction. As a part of the neural network model development effort, we derived a transport equation for drift velocity and then performed a budget analysis to conclude that an algebraic model for drift velocity in terms of the filtered variables that are resolved in a fTFM simulation is adequate, and the model should include the filtered gas-phase pressure gradient as a marker in addition to the filtered particle volume fraction and the filtered gas-solid slip velocity. Both a priori and a posteriori analyses reveal that the present model for drift velocity when used in a fTFM simulation is able to capture the fine-grid simulation results quite well. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract We have calculated in a closed form solution, in terms of modified Bessel function the first kind of order 0 and 1, for the motion of a positively charged particle in the magnetic field of an infinitely long, current-carrying wire in the nonrelativistic range. The orbits are not closed but exhibit a drift in the direction of the current with a speed that is independent of the launch angle. We found the drift velocity, drift displacement and the corresponding time, which we call the period. [ABSTRACT FROM AUTHOR]

A numerical technique to calculate real-space electron transport coefficients in gas under crossed electric and magnetic fields ($E \times B$ fields) by the propagator method (PM) was newly developed. Components of a centroid drift velocity vector of an electron swarm and its diffusion coefficients defined in the $E$ , $B$ , and $E \times B$ directions were calculated by applying the PM stepwise to the zeroth-, first-, and second-order $x$ , $y$ , and $z$ spatial moment equations derived from the Boltzmann equation. The results calculated for SF6 at $N = 10^{22}\,\,\text{m}^{-3}$ in $E/N$ and $B/N$ ranges of 100–1000 Td and 100–1000 Hx, respectively, agreed with those obtained by Monte Carlo simulations with discrepancies of a few percent. The Hall deflection of the drift velocity vector and the direction dependence of the diffusion coefficients were appropriately reproduced. A relaxation scheme developed for quick convergence of the electron velocity distribution function was effective also in the relaxations of the first- and second-order spatial moment distribution functions. A prototype of the PM as a calculation scheme to derive a set of electron transport coefficients necessary for fluid model simulations of magnetized plasmas was established. [ABSTRACT FROM AUTHOR]

The dispersal of drifting objects like plant propagule under wave action can provide important information for the restoration of the plant community in coastal areas. An improved motion equation of the drift under wave action is established by coordinate transformation under the premise that the buoyancy is always perpendicular to the free surface, considering the variation of submerged height and the pressure gradient. Its numerical solution obtained by the fourth order Runge-Kutta method was compared with the experimental results in the literature, and the rationality of the improved motion equation is then verified. Then the perturbation method and Lagrange tracking principle were used to obtain the average longitudinal drift velocity expressed by Stokes drift velocity. The effect of different forces in the motion equations to the longitudinal diffusive motion was analyzed. Finally, the hydrodynamic coefficients affecting the prediction were analyzed, and the results show that the effects of the added mass coefficient and the drag coefficient are mainly reflected in the region with higher wave heights. The findings may provide certain scientific guidance for the restoration of coastal vegetation ecology through natural colonization. • An improved motion equation of the drifting objects under wave-induced flow is established by considering the change of the submerged height. • The motion equation was numerally and analytically solved. • The effects of added mass coefficient and drag coefficient on drift velocity are analyzed based on the numerical solution. • The average longitudinal drift velocity was analytically obtained and the effect of different forces to motions was analyzed. [ABSTRACT FROM AUTHOR]

• Air-water bubble release experiments in upward inclinations from 3° to 89°. • Developed a new non-invasive method using computer vision to characterize Taylor bubbles. • Front velocity increases in pipe-to-annulus transition and tail velocity exhibits a transition behavior. • The Froude number characteristic dimension is better represented by the external ID for low inclinations and by the equi-periphery diameter for high inclinations. • Using the hydraulic diameter resulted in a 50% – 62% drift velocity underestimation in comparison with the experiments. The present study focuses on characterizing and modeling the Taylor bubble front and tail velocities in a pipe-to-annulus transition geometry. Air-water bubble release experiments in upward inclinations from 3° to 89° were performed in a 4-in (102-mm) ID pipe with a capped 3-in (76-mm) OD pipe inserted from downstream, forming a pipe-to-annulus transition. A new non-invasive method to measure liquid distribution using computer vision was developed. This method enables visualization of the liquid distribution and local measurements of Taylor bubble front and tail velocities. The Taylor bubble front velocity is dictated by drift, while the tail velocity is related to the liquid fallback rate and bubble coalescence. The drift velocity increased in the pipe-to-annulus transition, while the tail velocity exhibited a transition behavior. The Froude number characteristic dimension is better represented by the external ID for low inclinations and by the equi-periphery diameter for high inclinations. The typically reasonable approach of using the hydraulic diameter as the characteristic dimension resulted in a significant underestimation (50% – 62%) of drift velocity in the annulus for the experiments performed. The proposed model for drift velocity uses appropriate scales for the characteristic length and presented a mean average percentage error of 7.5%. [Display omitted] [ABSTRACT FROM AUTHOR]